If you create your promo code from the above link, you will get 1GB bonus data with 30 days validity

you can create a promo code using an invitation link from one of your skitto friends

If you create your promo code from an invitation link, you will get 2GB bonus data with 30 days validity

By the way, you can only use ONE promo code to buy your skitto SIM. Also, promo codes can only be applied before you buy the SIM. If you create a promo code after you have already activated your SIM, you will not be able to use that code.